1. Field of Use
This invention relates generally to hydraulic excavator machines or the like having pivotally movable components and to self-contained electrohydraulic individual power units for driving the components.
2. Description of the Prior Art
Large excavating machines, such as hydraulic mining shovels or the like, typically comprise a self-propelled carrier having driven and steerable crawler tracks and a horizontally rotatable upper section is mounted on the carrier. A boom is pivotally mounted on the carrier, a stick is pivotally mounted on the boom, a shovel is pivotally mounted on the stick, and double-acting hydraulic cylinders are provided for moving the boom, stick, and shovel. Typically, the boom cylinder is pivotally connected between the frame of the upper section and the boom to operate the latter; the stick cylinder is pivotally connected between the boom and the stick to operate the latter, and the shovel cylinder is pivotally connected between the stick and the shovel to operate the latter. Heretofore, the hydraulic fluid for operating these cylinders was supplied by an internal combustion engine-driven main hydraulic pump which was mounted on the upper section. Hydraulic fluid was carried between the main pump and the individual cylinders, as required, through large flexible high pressure fluid carrying hoses extending between the cylinder and the main pump, and the necessary valving was located either on the upper section of the machine, or, when necessary, on the individual cylinders. In some cases, control valves located on the cylinders required additional control fluid hoses or lines, or, if solenoid-operated, required electrical control wires.
Presently, excavating machines are required which are substantially larger and heavier and have a greater load-carrying capacity than was formerly the case. For example, some excavating machines weigh 662,000 pounds and require a hydraulic power rating of 1,000 horsepower with hydraulic fluid being supplied at pressures up to 4,350 psi at flow rates of up to 423 gallons per minute. In such machines, it is necessary to use very large valves, pipes, and fluid hoses between the hydraulic cylinders and the main pump and this becomes very complex and costly. In some instances, hoses having flexible reinforced coverings, valves, and piping are not obtainable in the sizes as large as required, or, if obtainable, are extremely expensive and are not sufficiently reliable in view of the large pressures involved. Furthermore, when hydraulic power, fluid pressure, and rate of fluid flow in large systems exceeds certain values, flow resistance increases at a geometric rate thereby resulting in a net loss of power available at the cylinders and requiring expenditure of greater energy. In addition, in large conventional systems, substantial amounts of energy are required to accelerate, decelerate, reverse, and reaccelerate fluid flow.
The prior art contains examples of a combined motor-driven hydraulic pump and hydraulic cylinder unit which is employed to effect relative movement between two components and U.S. Pat. No. 3,608,742 exemplifies an elementary arrangement which, however, differs from that hereinafter described.